1. Field of the Invention
This invention relates generally to an exciter for electrical generators and, in particular, to an improved exciter armature design.
2. Background of the Art
Generators are well known for converting mechanical energy to electrical energy. Generators commonly include an exciter mounted at one end of the generator rotor shaft. The exciter produces an output current, such as three-phase A.C. current, which is rectified and supplied to the field windings of the generator. Known exciters typically include a stator fixed to a housing and an armature assembly mounted on or rotatably coupled to the rotor shaft. Conductive windings are disposed in slots in the outer periphery of the armature assembly. The windings are rotated through a D.C. magnetic field established by the stator, thereby producing the A.C. output current in accordance with well-known electromagnetic principles.
The armature assembly forms part of the flux circuit and it also acts as the support structure for the conductive windings. More particularly, during exciter operation, centrifugal forces act to force the windings outward from the generator shaft. If the windings are not properly supported, these forces will distort armature symmetry and induce undesirable vibrations.
To alleviate this problem, the winding slots commonly incorporate support structure in the form of support wedges. Alternatively, semi-closed slots or fully closed slots are sometimes employed to further support the windings. However, these winding slots lend no support to the winding end turns-the portion of a winding which extends beyond the armature stack. In order to support the end turns, it is known to employ end bands constructed of fiberglass or other nonferromagnetic material. Because the end bands are installed after armature winding, it is difficult to ensure concentricity of the end bands and end turns. Additionally, it is difficult to maintain symmetry during exciter operation because the end bands are not secured to the rest of the armature assembly or the rotating shaft. These factors make vibration a continuing problem in conventional exciter designs.
U.S. Pat. No. 4,900,959 to Drinkut et al. attempts to overcome some of the problems set forth above. The Drinkut design is not suitable for many applications because of the excessive size of the retaining cylinder required to provide adequate winding support. Additionally, such a design is difficult to mount in any location other than the end of the rotating shaft.